1. Field of the Invention
This invention relates to the activation of catalysts used for preparing halogen-substituted hydrocarbons and more particularly to the activation of supported noble metal catalysts used for fluorohalocarbon or fluorohalohydrocarbon hydrodehalogenation.
2. Background
Useful catalytic processes have been developed for replacing non-fluorine halogen atoms with hydrogen in halogen-substituted hydrocarbons containing fluorine. U. K. Patent Specification 1578933, for example, discloses the production of tetrafluoroethane (as well as certain organic by-products) characterized in that certain halogenated ethanes containing four or five fluorine atoms are reacted with hydrogen at elevated temperatures in the presence of a hydrogenation catalyst. The use of catalysts consisting of palladium supported on charcoal and catalysts consisting of palladium supported on alumina are exemplified in particular. U.S. Pat. No. 4,873,381 discloses a process for the manufacture of 1,1,1,2-tetrafluoroethane by the vapor phase hydrodehalogenation of 1,1,1,2-tetrafluorochloroethane in the presence of a catalyst consisting essentially of palladium on an aluminum fluoride or fluorinated alumina support.
Supported noble metal catalysts have been used for many years as catalysts for certain reduction, hydroforming and hydrogenation processes and the like. A common problem encountered in these processes has been a decrease in catalytic activity over time. Since these catalysts are relatively expensive, it is clearly advantageous to regenerate them rather than replace them. Accordingly, processes for regenerating catalysts for various processes have been developed. For example, U.S. Pat. No. 4,164,481 is directed to a process of regenerating a noble metal catalyst used in the reduction of organic nitro compounds.
Many factors are involved in the deactivation of a catalyst. Deactivation has been attributed to various causes including sintering, poisoning of active sites, physical deterioration such as crumbling, and coking. The exact cause of the catalyst activity degeneration and its effects on a process depend on the nature of the process.
Activity regeneration for reforming catalysts has been studied for many years. Elaborate and costly procedures are typically required to restore catalyst activity. For example, J. P. Franck and G. Martino in "Progress in Catalyst Deactivation," ed. by J. L. Figueiredo, Martinus Nkjhoff, The Hague, 1982, p. 386 ff, describe a normal regeneration procedure for reforming catalysts which involves four stages. The first stage usually involves cooling the catalyst to some lower than operating temperature (about 200.degree. C.), followed by removal of hydrocarbons and hydrogen by nitrogen. The second stage involved elimination of coke by combustion at 380.degree. C. to about 500.degree. C. During this stage it may be necessary to inject HCl, CCl.sub.4, 1,2-dichloropropane or any other halogenated hydrocarbon which will produce HCl, during the combustion phase. The third stage involves restoration of catalyst acidity by increasing its chlorine content, in the form of HCl or a chlorinated compound such as CCl.sub.4, to the desired level at about 500.degree. C. in the presence of air. The last stage usually involves treating the catalyst with chlorine and oxygen at about 510.degree. C.-530.degree. C. in order to redisperse the platinum crystallites.
Various methods of activating catalysts using chlorine are disclosed in U.S. Pat. No. 2,851,398; U.S. Pat. No. 2,906,702; U.S. Pat. No. 3,134,732; U.S. Pat. No. 3,147,229; and German Offen. DE 2,009,114. However, these methods do not address catalyst activity for hydrodehalogenation of halogensubstituted hydrocarbons containing fluorine and at least one other halogen.